1. Field of the Invention
The present invention relates to a plasma display device.
2. Description of the Related Art
An AC plasma display device (PDP) comprises two opposed glass substrates, a plurality of address electrodes, arranged on one of the glass substrates, parallel to each other, and a plurality of sustain electrodes, arranged on the other glass substrate, to extend parallel to each other and perpendicular to the address electrodes. The sustain electrodes include alternately arranged X-electrodes and Y-electrodes. A display cell is formed between an X-electrode and a Y-electrode which are adjacent to each other.
In one display cell, a writing voltage pulse is supplied between the address electrode and the Y-electrode to cause electric discharge to generate a priming, and a sustain discharge voltage pulse is supplied between the X-electrode and the Y-electrode to sustain the discharge to illuminate the display cell.
The X-electrodes are classified into odd number X-electrodes and even number X-electrodes, which are connected to respective X-electrode sustain pulse generating circuits. The Y-electrodes are connected to an H side circuit and an L side circuit of a Y-electrode sustain pulse generating circuit via a scanning driver. The scanning driver has ground terminals (GND) and high voltage terminals (HVcc); the H side circuit is connected to the ground terminals, and the L side circuit is connected to the high voltage terminals. The address electrodes are connected to an address electrode pulse generating circuit. Respective pulse generating circuits are mounted to printed circuit boards and connected to the address electrodes and the sustain electrodes (X-electrodes and Y-electrodes) on the glass substrate via printed circuit boards and flexible printed circuit boards (FPC).
The above described type AC plasma display device is disclosed, for example, in Japanese Unexamined Patent Publications No. 9-160525, No. 11-327503 and No. 11-327458.
FIGS. 13 and 14 show the prior art. In FIGS. 13 and 14, there are intermediate circuit boards 38H and 40H between a printed circuit board 36H and a plasma display panel, and connectors 42H are provided for the intermediate circuit boards 38H and 40H. The connector 42H has pins 43a and 43b provided on a part of the intermediate circuit boards 38H and 40H, and holes 36a and 36b provided in the printed circuit board 36H. In the connector 42H, a group of the terminals 43a-36a for the odd number X-electrodes and a group of the terminals 43b-35b for the even number X-electrodes are arranged such that the connector 42H is roughly divided into two portions. An arrow 44H shows a line, regarding a specific odd number X-electrode 18x, which is laid from the first (odd number) sustain pulse generating circuit 24H to the odd number X-electrode 18x on the glass substrate 14 via the printed circuit board 36H, the connector 42H and the intermediate circuit board 38H. In this case, the line 44H greatly extends round upward, and the line length of the conductor is increased. Accordingly, the impedance becomes higher. The printed circuit board 36H is a multi-layered printed circuit board having two conductor pattern layers 36p and 36q. 
As the size of the plasma display device is increased, the size of the glass substrates is increased. Accordingly, a difference between the size of the glass substrates and that of each printed circuit board is increased. As a result, it becomes difficult to connect the X-electrodes and Y-electrodes with the printed circuit boards concerned. For example, in the case where the length of one side of the printed circuit boards relating to the X-electrodes and the Y-electrodes is 30 cm and the length of one side of the glass substrates is 50 to 70 cm, it becomes difficult to connect the terminals of the printed circuit boards with the X-electrodes and the Y-electrodes without causing any problems. In order to solve the above problems, it is preferable that an intermediate circuit board is provided between the printed circuit board and the X-circuit board and also between the printed circuit board and the Y-circuit board. The conductor pattern on the printed circuit board and that on the intermediate circuit board are connected with each other by a connector.
In the connector provided between the printed circuit board for the X-electrodes and the intermediate circuit board, as shown in FIGS. 13 and 14, a group of the conductor patterns connected to the printed circuit board for the first X-electrodes extend to the first portion of the connector, and a group of the conductor patterns connected to the printed circuit board for the second X-electrodes extend to the second portion of the connector. That is, in the connector, a group of the terminals for the odd number X-electrodes are arranged, and a group of the terminals for the even number X-electrodes are arranged next to them. Due to the above arrangement, the connector can be easily connected. In the same manner, concerning the Y-electrodes, there are provided a group of the terminals connected to the Y sustain pulse generating circuit H side circuit and a group of the terminals connected to the Y sustain pulse generating circuit L side circuit.
However, the following problems occur; according to the positions of the terminals of the X-electrode and the Y-electrode, a distance between the sustain pulse generating circuit and the connector terminals and a distance between the connector terminals and the X-electrode are changed. Accordingly, the lengths of the lead lines communicating with the X-electrodes and Y-electrodes located at specific positions are increased. As a result, the impedance becomes higher. Therefore, the impedance fluctuates and also the voltage drop fluctuates in the case of discharge. Accordingly, the time and intensity of sustain discharge fluctuate greatly, which causes unevenness on the display and further causes a difference in luminance at each position on the display, that is, the quality of the display is deteriorated.
An object of the present invention is to provide a plasma display device by which the quality of display can be enhanced, by reducing the fluctuation of impedance.
The present invention provides a plasma display device comprising a plasma display panel having at least a plurality of sustain electrodes for emission of light, a printed circuit board having a first sustain pulse generating circuit for supplying a first sustain discharge pulse to a first group of electrodes in the plurality of sustain electrodes and a second sustain pulse generating circuit for supplying a second sustain discharge pulse to a second group of electrodes in the plurality of sustain electrodes, and at least one intermediate circuit board arranged between the printed circuit board and the plasma display panel to connect the sustain pulse generating circuits to the sustain electrodes, wherein the printed circuit board and at least one intermediate circuit board are connected to each other by at least one connector, the connector including a first set of terminals connected to the first sustain pulse generating circuit and a second set of terminals connected to the second sustain pulse generating circuit, the terminals of the first and second sets being arranged in a row alternately one by one or one group by one group.
According to this structure, with respect to the X-electrodes and Y-electrodes arranged at specific positions, fluctuation of the length of the leads can be reduced and also fluctuation of the impedance of the leads can be reduced. As a result, unevenness on the display, which looks like mold, can be suppressed, and further a difference in brightness at each position of the display cell is not increased. Therefore, the quality of display can be enhanced.
It is preferable that the printed circuit board comprises a multi-layered printed board. It is more preferable that the printed circuit board comprises a multi-layered printed board having four conductor pattern layers or having not less than four conductor pattern layers. When the multi-layered printed board is used, it is possible to increase the line width of the lead. Therefore, the impedance can be reduced.